Group B Strep Culture

Reviewed by Neha Pathak, MD on March 19, 2021

Who Gets the Test?

All women who plan on delivering vaginally will get tested for group B strep during pregnancy. Some doctors do not test women who are planning to deliver by C-section.

What the Test Does

Group B strep is a common type of bacteria that lives in the vagina or the rectum. About 1 out of 4 people carry it. It's usually harmless, and does not cause infection. However, during birth, you could pass the bacteria to your baby, which could cause pneumonia or other problems. Testing for the bacteria -- and getting treated with antibiotics if you need them -- will help keep your baby safe.

How the Test Is Done

Your doctor will use a cotton swab to get a sample from your vagina and rectum. The test is safe and painless.

What to Know About Test Results

You'll get results in a few days or so. If you test positive, don't worry. Your doctor will give you antibiotics during labor that will protect your baby.

Despite the similar name, group B strep is not related to strep throat.

How Often the Test Is Done During Your Pregnancy

You will get the test once at 35 to 37 weeks, shortly before your due date. Some women don't need the swab because they already know that they're positive. They automatically get antibiotics during birth.

Show Sources


CDC: "Group B Strep: Prevention in Newborns."

American Congress of Obstetricians and Gynecologists: "Group B Streptococcus and Pregnancy."

© 2019 WebMD, LLC. All rights reserved. View privacy policy and trust info